Clinical lead Dr Keogh (William Beck) is among the staff gathered outside the hospital in the trailerThe staff of Holby City Hospital are in the midst of an explosive disaster and faced with life-or-death emergencies in a first look at the Casualty 40th anniversary episodes. An eerie chorus of children singing “Happy Birthday dear dad” can be heard as members of the emergency department, including clinical lead Dr Keogh (William Beck), gather outside the hospital. The trailer does not reveal much, ending with a clip of what appears to be armed police officers approaching Holby City Hospital. The show, which has been filmed at Cardiff’s BBC Roath Lock Studios since 2011, is also expected to move to a new fictional hospital in Wales next year. The Casualty 40th anniversary episodes will air on September 5 on BBC iPlayer and BBC One.